1. Field of the Invention
The present invention relates to a multilayer nanocrystal structure and a method for producing a multilayer nanocrystal structure. More specifically, the present invention relates to a multilayer nanocrystal structure with high luminescence efficiency, superior optical stability and superior chemical stability, the multilayer nanocrystal structure comprising: a nanocrystal alloy core including an alloy interlayer, two or more nanocrystals formed at the interface between the two or more nanocrystals, and one or more layers of nanocrystal shells formed sequentially on a surface of the nanocrystal alloy core; and a method for producing the multilayer nanocrystal structure.
2. Description of the Related Art
A nanocrystal is defined as a material having a crystal size at the nanometer-scale level and composed of several hundred to several thousand atoms. Since such a small-sized nanocrystal has a large surface area per unit volume, most of the constituent atoms of the nanocrystal are present on the surface of the nanocrystal. Based on this characteristic structure, the nanocrystal exhibits quantum confinement effects, and shows electrical, magnetic, optical, chemical and mechanical properties that are different from the properties of bulk materials comprised of the constituent atoms used in the nanocrystal. That is, control over the physical size of nanocrystals enables the control of the properties of the nanocrystals.
Vapor deposition processes, including metal organic chemical vapor deposition (“MOCVD”) and molecular beam epitaxy (“MBE”), have been used to prepare nanocrystals. More recently, wet chemistry techniques wherein a precursor material is added to an organic solvent to grow a nanocrystal have advanced significantly. According to the wet chemistry technique, as a crystal begins to grow, a dispersant coordinates to the surface of the crystal to control the crystal growth. Accordingly, the wet chemistry technique has an advantage in that nanocrystals can be uniformly prepared in size and shape in a relatively simple manner at low cost, compared to conventional vapor deposition processes, e.g., MOCVD and MBE.
A core-shell structured semiconductor nanocrystal with increased luminescence efficiency, and a method for preparing the semiconductor nanocrystal, are disclosed in U.S. Pat. Nos. 6,322,901 and 6,207,229, respectively. The core-shell structured semiconductor nanocrystal was reported to show improved luminescence efficiency while the luminescence wavelength of the core is essentially maintained due to passivation effects from the shell structure which contribute to reduction in defects on the surface of the core, and quantum confinement effects. However, the method for preparing the semiconductor nanocrystal has disadvantages in that relatively small-sized nanocrystals are necessarily used as a core and the small-size nanocrystals disadvantageously aggregate due to their instability upon formation of the shell. A shell whose surface has an insufficient thickness is unstable and is not therefore sufficiently passivated, and thus has the disadvantages of both low optical stability and poor chemical resistance.